A paper, entitled "Hydrometallurgical Recovery or Removal of Arsenic From Copper Smelter By-products" by K. Togawa, Y. Umetsu and T. Nishimura, presented at the 107th A.I.M.E. annual meeting at Denver, Colorado on Feb. 27-Mar. 2, 1978, discusses the problems involved in recovering valuable metals from copper ore refining flue dust, as well as the removal of arsenic as insoluble arsenates and as arsenic sulfide from aqueous solutions, and the hydrometallurgical recovery of arsenic trioxide from arsenic sulfide. The paper recovery from the flue dust of metals uncontaminated with arsenic, or the recovery of arsenic as a saleable product, nor does it disclose the other advantages or objectives of the present process.
An earlier article entitled "Recovery of Metals from the Dusts of Flash Smelting Furnace" by Eikichi Mohri and Minoru Yamada presented at the World Mining and Metals Technology Proceedings of the Denver Joint MMIJ-AIME meeting in 1976 discloses a hydrometallurgical process for treating copper smelter dusts by leaching, precipitating some (but not all) copper with hydrogen sulfide, neutralizing to pH2 with calcium carbonate to prevent precipitation of iron arsenate during subsequent copper cementation with iron powder, and finally oxidizing the solution with blowing air to form a stable iron arsenate. This process does not overcome the necessity for handling arsenic in its dangerous soluble forms during metal recovery steps, as does the present invention, nor does it immobilize arsenic in an insoluble state early enough so that substantially complete copper recovery is possible (H.sub.2 S precipitation must be halted at 2-3 grams of copper per liter of solution to avoid precipitating arsenic with the copper in this process). Neither does it provide for the recovery of arsenic in saleable form as sodium arsenate. The present process overcomes these problems and allows for substantially complete recovery of copper, zinc, cadmium, lead, and other metals, as well as sodium arsenate.
U.S. Pat. No. 4,149,880 to Prater, et al., discloses a copper cementation process following an oxygen pressure leach of the ore wherein some arsenic is insolubilized and about 0.5 to 2.0 grams per liter arsenic remain in solution. In this process, no attempt is made to insolubilize essentially all the arsenic value as is done in the present process.
U.S. Pat. No. 2,686,114 to McGauley, et al., discloses the insolubilization of arsenic values in a high pressure, high temperature ore oxidation leach using air. Arsenic is precipitated with iron in the ore and with alkaline earth metals as arsenates of these metals. The advantages of total insolubilization of arsenic with ferric ions apparently are not known to these inventors.